502 REPORT— 1873. 



unmistakable evidences of what is going on ; we get an idea of what forces 

 are at work. But spots are not alone in question. 



I say a few words with reference to some of the proposed lines of obser- 

 vation. 



Prominences at Limb. 



1. This is clearly necessary. We must have a prominence-curve as well as 

 a sun-spot one. 



2. In this way we shall be able to do for prominences what Carrington 

 has done for the distribution of the spot in latitude, and in time settle another 

 question about which there is much contradictory assertion among foreign 

 observers at present. 



3. For this perhaps C and brilliancy at base should be universally adopted. 

 It will doubtless prove of much importance ultimately to keep to the division 

 of prominences I have proposed in a paper communicated to the Royal 

 Society. 



4. Some one line in the case of each element must be taken and kept to. 

 These observations have already given me much evidence of this kind — 



a, 



a + b, 

 a-\-b + c, 

 a + b-}-c + d; 



and the series should be extended as far as possible. The structure of the 

 solar and stellar atmospheres cannot be got at in a more convenient manner 

 than this at present ; and as the lines indicate the vapours above the highest 

 level of the photosphere we may look for secular changes. 



6. I have already evidence, I think, of change since 1868. 



Prominences on Sun. 



7, 8, 9, 10, 11. The observations are complementary to those made at 

 the limb. 



12, 13. I have already detected changes which are probably connected with 

 the sun-spot period. 



18, 19, 20. I have already detected changes. 



I think these observations should be made over one of the 11 -year periods, 

 under absolutely the same conditions, with the same eyes and instruments, if 

 possible ; and even after that time I would rather extend the programme than 

 alter it. The value of each observation will be increased by each additional 

 similar observation. 



Of course I expect the chemical end of the spectrum to be photographed. 

 Rutherford and Cornu have shown this to be perfectly feasible in the case of 

 18, 19, 20. I believe that time and money are alone wanted to do part of 

 all I have put down by photography. It will be an immense gain if this 

 can be done from F, for the region between F and G is terribly trying for 

 the eye. Up to F the eye must naturally be depended on. 



Of associated work there will be such researches as explain to us what the 

 various phenomena mean ; measures of solar diameter ; photographs of sun- 

 spots on a large scale ; and eye-observations with a fine instrument to deter- 

 mine whether the changes I have pointed out in the spectra and appearance 

 of sun-spots are connected with the sun-spot period. 



I hope my accidental connexion with the new method of work will not 

 cause me to be considered presumptuous if I state my opinion, that if it is 



